The dynamic range of a typical CMOS image sensor is between 65 and 75 dB. The scene dynamic range, however, may extend over more than 5 orders of magnitude. If the scene dynamic range exceeds the sensor dynamic range, then portions of the image may be clipped or distorted in the darkest or brightest areas of the scene.
Techniques for extending dynamic range have included using both non-linear sensors and linear sensors. The non-linear sensors may cause image lag, have a large pixel size, cause inflexible or destructive compression, loss of contrast, increased noise or long integration time. Linear sensors may have excellent contrast and improved noise processing. They may also produce excellent opportunities for post-processing, since the output is typically directly related to the input.
A high dynamic range linear sensor often takes several integrations of the same scene. Each integration has a different integration time. The varying sensitivity of the different integrations can provide more information about the scene. When each integration is completed, each pixel may be accessed several times to obtain all the information, which may decrease the frame rate of the sensor. A frame memory may also be necessary to temporarily store the results of the integration.